Preparation of cellulose solutions



Patented July 26, 1932 PATENT OFFICE HARRY P. BASSETT, OF CYNTHIANA, KENTUCKY PREPARATION OF OELLULOSE SOLUTIONS No Drawing.

This invention relates to the preparation of cellulose solutions and more particularlyto a process of preparing cuprammonium solutions of cellulose. The principal object of this invention 1s to provide a simple, efficient and connnercially practical process of preparing cuprammonium solutions of cellulose wherein the amount of copper required is substantially less than in similar processes heretofore em ployed.

Other objects and advantages of the 111- vention will become apparent during the course of the following description.

As is well known, one of the customary Ways of preparing solutions of cellulose, such as those which are employed in the spinning of artificial silk, artificial straw, artificial horse hair and the like, is to dissolve cellulose material in a solution resulting from mixing copper hydroxide and ammoma. This solution maybe efiected in various ways but I have noW discovered that the amount of copper required for use in these prior processes may be substantially reduced by modifying the known procedure in accordance with our present invention. This 1s particularly important from a commercial standpoint since it effects a real economy and at the same time substantially eliminates the heretofore encountered trouble in spinning artificial silk due to the deposition or collecting of particles of colloidal copper in the spinnerettes. Heretofore, the excesslve amount of combined copper in the cuprammonium solutions has resulted in the liberation of small amounts of copper hydroxide in colloidal form and it has repeatedly been observed that these particles collect in the spinnerettes and deleteriously affect the spinning operation. I have found that this condition is substantially avoided in the spinning of cuprammonium solutions prepared in accordance with my present process.

5 In the preferred practice of my process relatively pure cellulose material such as cotton linters, purified wood pulp or the like, is introduced into a beater engine of the character employed in the paper industry. This heater may be of any conventional type,

Application filed February 13, 1930. Serial No. 428,242.

the beater itself forming no part of the present invention. The pulp is mixed with a great excess of water and this is preferably accomplished by first introducing the water into the beater and adding the pulp thereto. The amount of Water used may be in approximately the same amount in Which it is used in the manufacture of paper. For example, it is advantageous to use such an amount of water in relation to the amount of pulp that a suspension of approximately 4 or 5 per' cent. of pulp in water is provided. In any case, the water should be in great excess. The suspension of pulp in water is then circulated around the beater and subjected to the action of the usual beating roll for approximately from one-half hour to five hours depending upon the condition of the cellulose material originally employed. In commercial practice beating for approximately two hours is ordinarily suflicient. The purpose of the beating operation is to break up the cellulose material into minute fibers and to hydrate the cellulose.

After the desired degree ofbeating has been completed a sufficient amount of alkali is added to the beater, which is preferabl kept operating, to react with a copper sa t later added to precipitate on the cellulose in the beater, the theoretical amount of copper, in the form of copper hydroxide, required to effect the desired cuprammonium solution. In commercial practice, it is ordinarily desired that approximately .39 of a pound of copper, computed as metallic copper, shall be precipitated on each pound of cellulose present.- The amount of combined copper required to be present in association with the cellulose may vary in different processes and in different plants but it is obviously within th province of one skilled in the art to modify the proportions of reacting ingredients to provide the desired proportion of copper with respect to the cellulose. While numerous alkalies may be added to the beater, as will be apparent, I prefer to employ caustic soda since this material is readily available and readily reactswith copper sulfatewhich is the copper salt which We prefer to employ in the formation of the copper hydroxide.

However, it will be apparent that in place of the two reacting ingredients specified any other soluble compounds may be used which will react to form copper hydroxide.

As stated above, after the desired. degree of beating of the cellulose material has been completed, sodium hydroxide in solution is then preferably added to the beater. The strength of the sodium hydroxide solution is of no practical importance, nor is the amount added providing that there shall be in the beater at least enough sodium hydroxide to react with all the copper sulfate to be added subsequently. However, in commercial practice I prefer to employ a 20 per cent. solution of sodium hydroxide .and to add a reasonable excess of the solution over the theoretical amount required to react with the copper sulfate. The copper sulfate is then added preferably in water solution very slowly, as from a capillary tube, just at the point where the mass in the beater enters the wheel or beater roll. The concentration of copper sulfate in the water solution is unimportant but for practical use I find that a. strength of 20 per cent. CuSO...5H O is most convenient. The amount of copper sulfate employed should be, as stated, sufficient to give .39 of a pound of copper, computed as metallic copper, .to each pound of cellulose used.

In view of the fact that the cellulose material will become impregnated with the alkali solution in the beater and will, in turn,

become impregnated with the copper solution added, the precipitation of the copper hydroxide as a result of the reaction will take place in and on the cellulose material whereby it will be thoroughly impregnated with particles of copper hydroxide. 7

Under ordinary conditions, the treatment described may be conducted at atmospheric temperatures but in summer in warm climates it may be found advisable to cool the mass in the beater slightly, as by the addition of ice or by means of cooling coils.

The treatment described may be modified by adding the copper sulfate solution to the beater and adding the alkali later providing that the temperature of the mass in the beater is kept low, say below 15 C., but this practice is not recommended for large scale/operation as there is. atendency toward deco-mposition of the copper compound by local beating.

After the mass .has been treated'i-n the manner described, the operation of the beater engine is suspended and the mass is then drawn oii and centrifuged to remove the .ex-

cess of liquid present. The remaining'solid,

hydroxide or the like remaining in the -cel-lu-' lose material.

The resulting material consists of cellulose impregnated with copper hydroxide.

The material is then introduced into any form of conventional dissolver or other device provided with a kneading agitator and aqua ammonia is added to the mass which is preferably being agitated at the time. Ordinarily, a 26 or 28 per cent. solution of ammonia is employed and sufiicient material is added to provide 1 pound of ammonia, computed as NH to each pound of cellulose present. Obviously, the amount of ammonia may be varied but it is standard practice to employ the ammonia in the proportions specified. The resulting mass is agitated for from forty-five minutes to three hours, and preferably two hours, to effect the complete solution of the cellulose in the cuprammonium solution. Care must be taken to keep the temperature of the mass relatively cool and preferably not in excess of 15 C. After the desired period of the treatment, the solution may be diluted with water as desired to bring the solution to the desired strength for spinning. This treatment is conventional.

As will be apparent, the solution of cellulose is readily effected due to the intimate association of the copper hydroxide with the cellulose. Moreover, in view of this intimate association the excess of copper required by prior processes need not be employed in the present process. In fact, commercial practice has demonstrated that the present process results in the saving of approximately from 25 to 33 per cent. of the copper used in the customary processes of similar nature. The economy of the process is, therefore, readily apparent.

In the interest of describing a specific embodiment of the present invention, the following procedure may be considered as illustrative of the invention:

Approximately 10 pounds of relatively pure cotton linters are added to a beater containing approximately gallons of water. This mass is circulated in the beater for approximately 2 hours and thereafter approximately 25 pounds of commercial caustic soda diluted to a strength of 20 per cent. NaOI-l are added to the mass which is being maintained in circulation. Thereafter approximately 15 pounds of copper sulfate dissolved in pounds of water are added to the mass from a capillary tube at the point where the mass enters the beater roll or wheel. Thereafter, the mass is drawn off, freed from the excess liquid present, washed with water until free from impurities and introduced into a conventional dissolver. Approximately 38.5 pounds of a. 26 per cent. solution of ammonia are added and the mass is then subjected to a kneadingagitation for approximately two hours. Thereafter, the solution maybe diluted in accordance with conventional practice to the desired degree.

The preferred procedure described may be modified without unreasonably decreasing the efiiciency of the process by omitting the addition of alkali and copper salt as separate steps and reacting such materials prior to their introduction into the beater. In this case, the copper hydroxide is formed outside of the beater and in order to secure the desired results the precipitated copper hydroxide should be stirred up in the reaction container in order to secure a temporary suspension of the copper hydroxide and this suspension should be added in a stream to the materials in the beater, preferably at the point where the mass enters the beater wheel or roll. While the association of the copper hydroxide with the cellulose material is not so intimate in this case as in the previously described embodiment wherein the copper hydroxide is formed in situ, it will be found that a relatively intimate association of the copper hydroxide with the cellulose material will be effected whereby the. desired amount of copper hydroxide will be mechanically retained by the cellulose material.

While I have described in detail the preferred embodiment of my invention it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

7 1. The herein described process of preparing cuprammonium solutions of cellulose which comprises intimately associating copper hydroxide with cellulose material while subjecting said cellulose material in liquid suspension to a mechanical beating action, removing the excess liquid from the resulting intimate mixture of copper hydroxide and cellulose material, thoroughly washing the resulting product to remove watersoluble material remaining in the cellulose material, and intimately mixing the washed product with ammonia to effect the solution of the cellulose material. V

2. The herein described process of preparing cuprammonium solutions of cellulose which comprises subjecting cellulose material in suspension in water to the action of a heater engine, impregnating the cellulose material with an alkali, slowly adding to the mass a compound of copper capable of reacting with the alkali to form copper hydroxide during the beating action, removing the excess liquid from the resulting cellulose material impregnated with copper hydroxide, thoroughly washing the resulting product to remove water-soluble material re maining in the cellulose material, and intimately mixing the washed product with ammonia to efiect the solution of the cellulose material.

3. The herein described process of preparing cuprammonium solutions of cellulose which comprises subjecting cellulose material in suspension in water to the action of a beater engine, adding an alkali to the suspension during the beating action, slowly adding to the mass at the point where it enters the beating wheel a compound of copper capable of reacting with the alkali to form copper hydroxide, removing the excess liquid from the resulting cellulose material impregnated with copper hydroxide, thoroughly washing the resulting product to remove water-soluble material remaining in the cellulose material, and intimately mixing the washed product with ammonia to effect the solution of the cellulose material.

4. The herein described process of preparing cuprammonium solutions of cellulose which comprises subjecting cellulose material in suspension in Water to the action of a beater engine, impregnating the cellulose material with caustic soda, slowly adding to the mass at the point where it enters the beater wheel a solution of copper sulfate, removing the excess liquid from the resulting cellulose material impregnated with copper hydroxide, thoroughly washing the resulting product to remove water-soluble material remaining in the cellulose material, and subjecting the washed product to a kneading agitation in the presence of ammonia to efl'ect the solution of the cellulose material.

In testimony whereof I affix my signature.

HARRY P. BASSETT. 

